This invention relates to an improvement of fault processing in a system which enables multiplex communication by connecting a sequence controller disposed at each work station to a communication line to perform addressing or channel division between the master station and each substation or between substations.
Heretofore, a system is available in which a plurality of sequence controllers are disposed at work stations in a factory and connected to one communication line in series, and these sequence controllers perform data communication between them to control industrial robots or numerical control machine tools.
In this communication system, each sequence controller is directly connected in series to one communication line, therefore, there was a problem of difficulty in fault location or decision of fault mode when a fault has arisen at a station or on an intermediate transmission line. Therefore, much time is required to perform fault location and fault recovery when it has occurred, and this forced the system to stop for many hours, thereby causing a great loss of productivity.
Further, damage caused by overvoltage or overcurrent in the communication equipment connected in series by a communication cable may spread over the whole system without localizing the damage.